The invention relates to a light-switching device which is reversibly switchable between at least a first state of reflecting light and a second state of absorbing light, said device comprising a stack of layers including a switchable layer of an optically switchable material which brings about a switch from the first state to the second state of the device by changing a density of hydrogen.
U.S. Pat. No. 5,905,590 describes a switching device comprising a switching film including hydrides of magnesium with other trivalent metals. By exchange of hydrogen, the switching film can be reversibly switched from a transparent state to a mirror-like state with zero transmission via an intermediate black absorbing state. The switching film is comprised in a stack of layers, which is deposited on a transparent substrate. By virtue of the optical effect, the device may be used as an optical switching element, for example as a variable beam splitter, optical shutter, and for controlling the illuminance or the shape of light beams in luminaires. The switching device may also be used for data storage and in optical computing, and in applications such as architectural glass, vision control glass, sunroofs and rear-view mirrors. By making a pattern in the switching film and providing the patterned switching film with transparent electrodes, a thin display can be manufactured.
It is a problem with these types of devices that they are relatively slow, because the speed of the switching effect is determined by the transport of hydrogen.
It is an object of the invention to provide a switching device, which has an improved speed. To this end, the invention is characterized in that the stack further includes a layer for storing hydrogen which comprises a material comprising essentially the same compounds as the switchable layer. The switching material has an excellent hydrogen storage capacity in the non-transparent state. Since the device is only switched between the reflective and the absorbing state, the hydrogen storage layer may be non-transparent and the switching material may be used for this purpose. In view of the high storage capacity of the switching material, the storage layer can be made thinner when the switching material is also used for the storage layer, which,leads to shorter diffusion times for the transportation of hydrogen and consequently a device with increased switching speed. Moreover, for switching between the reflecting and the absorbing state, less charge needs to be transported, i.e. less current is required for switching.
Advantageous embodiments of the invention are described in the dependent claims.
These and other aspects of the invention will be elucidated with reference to the embodiments described hereinafter.